A cotton thread fluidic device with a wall-jet pencil-drawn paper based dual electrode detector Nicol  o Dossi a, * , Rosanna Toniolo a , Fabio Terzi b , Nicola Sdrigotti a , Franco Tubaro a , Gino Bontempelli a a Department of Agrifood, Environmental and Animal Science, University of Udine, via Cotonificio 108, I-33100, Udine, Italy b Department of Chemical and Geological Science, University of Modena and Reggio Emilia, via Campi 183, I-41125, Modena, Italy highlights graphical abstract  Paper based wall-jet electrochemical detectors coupled with cotton-thread fluidic systems are proposed.  A pencil drawing approach was used to construct electrochemical detectors.  Dual electrode configuration of elec- trochemical detectors enables detec- tion of analytes with reversible behavior.  Simple and inexpensive methods for the detection of ascorbic acid and orthodiphenols are proposed. article info Article history: Received 17 May 2018 Received in revised form 21 June 2018 Accepted 22 June 2018 Available online xxx Keywords: Cotton thread electroanalytical devices Pencil-drawn electrodes Paper based dual electrochemical detectors Antioxidants Extra virgin olive oil Orthodiphenols abstract A simple and sensitive device is presented based on the use of pencil-drawn paper based electrochemical detector placed at the end of a cotton thread fluidic channel in wall-jet configuration. This innovative and fast responding electroanalytical system can be adopted for both single and dual electrode electro- chemical detection, this last achieved by applying two different potentials at two independent working electrodes drawn on the opposite faces of the paper based detector. Its performance was preliminarily optimized by adopting hexacyanoferrate(II) as probe species undergoing reversible electrochemical processes. These devices were then used for the single electrode detection of ascorbic acid in aqueous samples and the dual electrode detection of orthodiphenols in extra virgin olive oils (EVOOs). In fact, these devices enable hydrophilic orthodiphenols, typically present in EVOOs (extracted by a 80:20% v/v acetonitrile/water mixture), to be discriminated from hydrophilic monophenols instead present in almost all vegetable oils. Flow-injections runs were conducted by using a 0.01 M H 2 SO 4 þ 0.5 KCl running electrolyte allowing the rapid and selective detection of hydrophilic orthodiphenols with satisfactory sensitivity and a low enough detection limit (2 mM). Different real samples of EVOOs and sunflower oils were analyzed. Abundant enough contents of orthidiphenols were found in EVOO samples, while no trace of these antioxidants was found in sunflower oils. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Green Analytical Chemistry (GAC) stems from the use of dangerous chemical reagents and waste production, as well as from some undesired side-effects involved in conventional analytical * Corresponding author. E-mail address: nicolo.dossi@uniud.it (N. Dossi). Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca https://doi.org/10.1016/j.aca.2018.06.061 0003-2670/© 2018 Elsevier B.V. All rights reserved. Analytica Chimica Acta xxx (2018) 1e7 Please cite this article in press as: N. Dossi, et al., A cotton thread fluidic device with a wall-jet pencil-drawn paper based dual electrode detector, Analytica Chimica Acta (2018), https://doi.org/10.1016/j.aca.2018.06.061